Methods for using liquefied natural gas for well stimulation

ABSTRACT

A method for fraccing oil or gas wells to recover natural gas. Liquefied natural gas is vaporized to form a foam or dense fluid. The foam or dense fluid is compressed to high pressures. The high pressure natural gas foam or dense fluid is fed into the oil or gas well and once the well is pressurized to a pre-determined pressure and fracturing has begun, the flow of the foam or dense fluid is stopped. After a suitable period for fracturing to occur, the flow is reversed and the natural gas from the well and the foam or dense fluid fracturing fluid is recovered. The recovered and produced natural gas can be treated and made ready for use in other applications.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional application Ser. No. 61/650,588 file May 23, 2012.

BACKGROUND OF THE INVENTION

The invention relates to a method for stimulating oil wells with liquefied natural gas. More particularly, the invention provides for injecting natural gas into an oil or gas well to fracture the well and to assist in recovering the natural gas present in the well.

In the production of natural gas from shale or other “tight-gas” formations, hydraulic fracturing (or “frac”) is used to break up the rock around the well bore and reduce the resistance to gas flow. The frac technique generally requires injecting into the well large amounts of fluids that are compressible like nitrogen or carbon dioxide or incompressible such as water or liquefied petroleum gas. The fluids are pumped to high pressure to create large compressive forces around the well bore. These forces break the rock and create tiny fissures for gas flow. To aid in the penetration and stability of theses fissures, small amounts on the order of 1 to 2% by volume of hydrocarbons, mineral acids and “proppants” are added to the injected fluid. Thousands of tons of fluid may be injected during each frac job and much of this fluid is returned to the surface when the flow is reversed (hereafter called “produced fluids”) and natural gas is produced from the well.

If water is used as the fracturing fluid, the produced fluid water is typically brackish with small amounts of the other materials injected into the formation. Reuse of these waters is problematic because of their composition and consequently, the produced fluid water must be treated for environmental concerns and disposed of in surface waters. Alternatively, the produced fluid water must be injected into deep saline aquifers. If gases or condensable hydrocarbons such as liquefied petroleum gas are used, their availability and disposal after use can also create difficulties for the producer.

The invention addresses the problems associated with the disposal of producing fluid by using liquefied natural gas (LNG) as a fluid source. The produced fluid will have roughly the same composition of natural gas and can be introduced into a pipeline without further processing.

SUMMARY OF THE INVENTION

To address these concerns, the invention provides for a method for fracturing an oil or gas well to recover natural gas.

In one embodiment of the invention, there is disclosed a method for fracturing a well comprising the steps:

a) Vaporizing liquefied natural gas to form a foam or dense fluid; b) Compressing the foam or dense fluid and injecting into the well; c) Stopping the injection of the foam or dense fluid once a pre-determined pressure of the well has been reached; and d) Recovering the foam or dense fluid natural gas and product natural gas.

In another embodiment of the invention there is disclosed a method for fracturing a well comprising the steps:

a) Providing liquefied natural gas to a well site; b) Vaporizing liquefied natural gas to form a foam or dense fluid; c) Compressing the foam or dense fluid and injecting into the well; d) Stopping the injection of the foam or dense fluid once a pre-determined pressurization of the well has been reached; and e) Recovering the foam or dense fluid natural gas and product natural gas.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for a method for fraccing an oil or gas well to recover natural gas. Liquefied natural gas is shipped to the well site in large quantities such as about 1000 tons. The liquefied natural gas is rapidly vaporized utilizing a high-speed vaporization technique such as by a submersible combustion vaporizer or other known technique to form a foam or dense fluid. The vaporized liquefied natural gas which is essentially methane gas may be mixed with small amounts of additives such as a proppant. The proppant is any that may be typically used in fracturing such as treated sand or a man-made ceramic material.

The foam or dense fluid is then compressed by conventional techniques to pressures between 1000 and 10,000 pounds per square inch (psi) for injection into the well at rates ranging from 10,000 to 1,00,000 standard cubic feed (scf) per minute.

Depending upon the nature of the well and the composition of natural gas present in the well, carbon dioxide or nitrogen may be added to the liquefied natural gas prior to it being vaporized or before it is compressed for injection into the well such that the foam or dense fluid comprises more than just natural gas or natural gas plus one or more proppants.

Once the well has been fully pressurized to a pressure pre-determined by the operator and the fracturing process initiated, the flow of the pressurized natural gas is stopped. The foam or dense fluid will remain in the well for a time period necessary to assist in fracturing the well. The equipment that is employed to fed the foam or dense fluid is then reversed. The methane gas which is recovered is both the pressurized foam or dense fluid and methane present in the fractured well. This methane gas regardless of its origination is separated from the other produced fluids and proppants that may be recovered. The recovered methane gas whether it is from the foam or dense fluid used as the fracturing fluid or from the well proper can be fed directly to a pipeline where the methane can be sent to a storage facility or fed to another industrial operation. Alternatively, the recovered natural gas can be combusted and the combustion products run through heat exchangers, expanders or turbines to produce steam and/or electricity.

The methods of the present invention using natural gas from liquefied natural gas have numerous advantages over water or inert gas as fracturing fluids. Large amounts of water-based fracturing fluids, for example, can remain in the reservoir and reduce natural gas flow from the well. The vaporized liquefied natural gas used as a foam or a dense fluid is essentially the same composition as the in-situ natural gas present in the well. When fracturing is completed and the flow of the feed equipment is reversed, the produced fluids can be treated by the same equipment and in the same manner as the produced natural gas without having to perform any separation or purification steps as an operator would have to if other fracturing fluids are used. Further, no additional safety issues are created when the vaporized liquefied natural gas is fed into well as a foam or dense fluid.

While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims in this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the invention. 

Having thus described the invention, what I claim is:
 1. A method for fracturing a well comprising the steps: a) vaporizing liquefied natural gas to form a foam or dense fluid; b) compressing the foam or dense fluid and injecting into the well; c) stopping the injection of the foam or dense fluid once a pre-determined pressure of the well has been reached; and d) recovering the foam or dense fluid natural gas and product natural gas.
 2. The method as claimed in claim 1 wherein the well is selected from the group consisting of an oil well and a gas well.
 3. The method as claimed in claim 1 wherein vaporizing is performed by a submersible combustion vaporizer.
 4. The method as claimed in claim 1 wherein a proppant is added to the foam or dense fluid.
 5. The method as claimed in claim 1 wherein the foam or dense fluid is compressed to pressures from 1000 to 10,000 pounds per square inch.
 6. The method as claimed in claim 1 wherein the foam or dense fluid is fed into the well at rates from 10,000 to 1,000,000 standard cubic feet per minute.
 7. The method as claimed in claim 1 wherein the pre-determined pressure is a pressure at which fracturing of the well will occur.
 8. The method as claimed in claim 1 further comprising adding to the foam or dense fluid a gas selected from the group consisting of carbon dioxide and nitrogen.
 9. The method as claimed in claim 1 wherein the recovered foam or dense fluid natural gas and product natural gas is fed to storage, fed to another industrial operation, combusted or reused as the foam or dense fluid being fed to the well.
 10. A method for fracturing a well comprising the steps: a) providing liquefied natural gas to a well site; b) vaporizing liquefied natural gas to form a foam or dense fluid; c) compressing the foam or dense fluid and injecting into the well; d) stopping the injection of the foam or dense fluid once a pre-determined pressurization of the well has been reached; and e) recovering the foam or dense fluid natural gas and product natural gas.
 11. The method as claimed in claim 10 wherein vaporizing is performed by a submersible combustion vaporizer.
 12. The method as claimed in claim 10 wherein the well is selected from the group consisting of gas and oil wells.
 13. The method as claimed in claim 10 wherein a proppant is added to the foam or dense fluid.
 14. The method as claimed in claim 10 wherein the foam or dense fluid is compressed to pressures from 1000 to 10,000 pounds per square inch.
 15. The method as claimed in claim 10 wherein the foam or dense fluid is fed into the well at rates from 10,000 to 1,000,000 standard cubic feet per minute.
 16. The method as claimed in claim 10 wherein the pre-determined pressure is a pressure at which fracturing of the well will occur.
 17. The method as claimed in claim 10 further comprising adding to the foam or dense fluid a gas selected from the group consisting of carbon dioxide and nitrogen.
 18. The method as claimed in claim 10 wherein the recovered foam or dense fluid natural gas and product natural gas is fed to storage, fed to another industrial operation, combusted or reused as the foam or dense fluid being fed to the well. 